I spoted the source file where the actual renaming takes place, but I'm still looking for the location of the code responsible for handling the user interface and saving into the preferences... I'd be glad to prepare a patch if developers agree and point me to the right direction....

Thanks for taking the time to work on this. It's the best way to get things done, as I'm currently extremely busy working on my doctoral studies.

Rather than submitting a patch, why don't you use bzr and submit your changes using launchpad. That way, you will be an official contributor to the code. That is a very good outcome for the project and for you!

I didn't realize it was model specific. I assumed it wouldn't be. You can
find some samples 5D Mk II RAW files here:http://www.photographyblog.com/reviews_canon_eos_5d_mark_ii_3.php
If it becomes too difficult, one solution that will work (albeit slowly) is
to call exiftool and get it's results. I'm going to have to do that for
another feature request, which is to read metadata from MTS video files,bug #695517. So implementing that will in itself add a dependency on
exiftool.

The primary problem with the merged code last time was that it didn't match the design of the file renaming preferences. Things like stored values have very specific meanings. There are three levels of renaming: category, value, and formatting. A stored value is in the category sequence, and its value is a counter that increments and can be set in the user preferences, and its formatting is the number of digits it should take up.

I have already done the work to get exiftool working with MTS videos, but I'm not finished. The next step is to have exiftool be the default fallback option for all videos, as for some reason Fedora does not package hachoir metadata or kaa metadata. That means Fedora users currently cannot download videos using Rapid Photo Downloader. Using exiftool, they should be able to. I need to better integrate the exiftool code I've written. When I've done that, you can add the function to call the exiftool code for the file number. It should be really easy.